1. Field of the Invention
This invention relates to a plated copper alloy material to be used as a copper alloy wire, plate, etc. for electronic apparatuses and appliances, such as terminals, connectors and so forth.
2. Discussion of Background
As the plated copper alloy wire, plate, etc. for electronic apparatuses and appliances, for instance, there has so far been in much use of brass type or phosphor bronze type copper alloys, in the main, as the matrix, on which a plating is applied.
With regard to such plated copper alloy materials, there are various modes in their undercoat plating; that is, no undercoat plating is applied, copper plating is applied, or nickel plating is applied. In case the undercoat plating is applied, it is done under various conditions such that its thickness is varied, or others. With such background in mind, plated phosphor bronze type copper alloy forms the main current in the field of use where a relatively high reliability is demanded on the products, hence, depending on the level of demand on the adhesive reliability of plating, there have been used those undercoat plating formed under various conditions.
In recent years, with the electronic apparatuses and appliances tending to be miniaturized and to have high output capability, the circumstances, under which these electronic apparatuses and appliances are used, are becoming more and more stringent. For instance, with regard to connectors or the like, there is a problem of temperature rise due to their heat generation, etc. When the connectors, etc. are used in such circumstances of use, adhesion between the plating and the matrix becomes lowered, which may lead to exfoliation of the plating. As such, in recent years, much higher operating reliability is required of those parts for the electronic apparatuses and appliances of high output capacity.
As a method for manufacturing the plated contact element made of phosphor bronze and having high operating reliability, there has been proposed one, in which an undercoat plating of copper is thinly applied onto the matrix of phosphor bronze with use of a cyanide bath having a monovalent copper ion concentration of 10 to 60 g/l and an isolated cyanogen concentration of 10 to 20 g/l; thereafter tin or solder, as an overcoat plating, is electrically plated on this undercoat; and subsequently the entire combination of the matrix, the undercoat plating, and the over coat plating is subjected to heat-melting, or such tin or solder as the overcoat plating is melt-plated onto the matrix (vide: Japanese Unexamined Patent Publication No. 184482/1984).
With regard to the adhesive property of the copper alloy plating, it has been known that a fragile dispersion layer of Cu and Sn is formed in the neighborhood of the interface between the copper alloy and the plating, and Kirkendall voids are generated, due to mutual dispersion between copper in the copper alloy and tin in the plating, on account of which the adhesive property of the plating becomes lowered.
As for the influence of the undercoat plating on the heat-resistant adhesive property of the overcoat plating, the current situation is such that the nickel undercoat plating possesses the highest reliability, and that in case of the copper undercoat plating or in case where the undercoat plating is not provided, the heat-resistant adhesive property over a long period of time is relatively poor in its reliability. The nickel plating, however, has its characteristic of being relatively hard, while the matrix with the nickel undercoat plating having been applied onto it has a considerable disadvantage of tending to bring about cracks on the surface layer thereof during its shaping work by press, etc., hence it has a problem of being difficult to be utilized industrially.